Sapphire is presently being actively considered as screen for smart phones and tablets. It is the second hardest material after diamond so using it as screen would mean the smart phone/tablet has a superior scratch and crack resistant screen. Sapphire screen is already being featured in Apple iPhone 5S TouchID scanner and camera lens on the rear of the phone. Vertu, the luxury smartphone manufacturer, is also developing sapphire screen. However, since sapphire is the second hardest material, it is also difficult to be cut and polished. Coupled by the fact that the growth of a single large size crystal sapphire is time consuming, this results in long fabrication time and high fabrication cost. It is the high fabrication cost and long fabrication time of sapphire screen that limit Apple's use of such sapphire screen to only Apple Watch.
A current popular ‘tough’ screen material use is the Gorilla Glass made by Corning, which is being used in over 1.5 billion devices. Sapphire is in fact harder to be scratched than Gorilla Glass and this has been verified by several third party institutes such as Center for Advanced Ceramic Technology at Alfred University's Kazuo Inamori School of Engineering. On the Mohs scale of hardness, the newest Gorilla Glass only scores 6.5 Mohs which is below the Mohs value of mineral quartz. As such, Gorilla Glass is still easy to be scratched by sand and metals. Sapphire is the second hardest naturally occurring material on the planet, behind diamond which scores 10 on the Mohs scale of mineral hardness.
Mohs hardness test is to characterize the scratch resistance of minerals through the ability of a harder material to scratch a softer material. It matches one substance's ability to scratch another, and so it is a better indicator of scratch resistance than shatter resistance. This is shown in FIG. 1.
Following is quotations from ‘Display Review’ on sapphire screen:
“Chemically strengthened glass can be excellent, but sapphire is better in terms of hardness, strength, and toughness” Hall explained, adding “the fracture toughness of sapphire should be around four times greater than Gorilla Glass—about 3 MPa-m0.5 versus 0.7 MPa-m0.5, respectively.”This comes with some rather large downsides though. Sapphire is both heavier at 3.98 g per cubic cm (compared to the 2.54 g of Gorilla Glass) as well as refracting light slightly more.
So apart from being heavier, sapphire being the second hardest material is also a difficult material to cut and polish. Growing single crystal sapphire is time consuming especially when the diameter size is large (>6 inches), this is technically very challenging. Therefore the fabrication cost is high and fabrication time is long for sapphire screen. It is an objective of the present invention to provide fabrication means of sapphire screen materials that is quick to fabricate and low in cost while having the following advantages:                Harder than any hardened glass;        Less possibility of fragmentation than pure sapphire screen;        Lighter weight than pure sapphire screen;        Higher transparency than pure sapphire screen.For hardening of sapphire (Al2O3) thin film deposition, softening/melting temperature of softer substrate should be sufficiently higher than the annealing temperature. Most rigid substrates such as quartz, fused silica can meet this requirement. However, flexible substrate such as polyethylene terephthalate (PET) would not be able to meet the requirement. PET has a melting temperature of about 250° C., which is way below the annealing temperature. PET is one of the most widely used flexible substrates. The ability of transferring a substrate of Al2O2 (sapphire) thin films on to a softer flexible will significantly broaden its applications from rigid substrates like glass and metals to flexible substrates like PET, polymers, plastics, paper and even to fabrics. Mechanical properties of transferred substrate can then be improved. Therefore, Al2O3 thin films transfer from rigid substrate to flexible substrate can circumnavigate this problem of the often lower melting temperatures of flexible substrates.        